Polyolefins are useful in any number of everyday articles. However, one drawback to many polyolefins, especially propylene homopolymers and some propylene copolymers, is their relatively high glass transition temperature. This characteristic makes these polyolefins brittle, especially at low temperatures. Many applications of polyolefins benefit from having useful properties over a broad range of temperatures; consequently, there is a need to provide polyolefins that can maintain desirable characteristics such as high or low temperature performance, etc., while maintaining or improving upon the impact strength and toughness at lower temperatures. In particular, it would be advantageous to provide a propylene polymer possessing improved toughness and or high use temperature without sacrificing its other desirable properties.
Addition of a plasticizer or other substance to a polyolefin is one way to improve such properties as impact strength and toughness. Some patent disclosures directed to such an end are U.S. Pat. Nos. 4,960,820; 4,132,698; 3,201,364; WO 02/31044; WO 01/18109 A1; and EP 0 300 689 A2. These disclosures are directed to polyolefins and elastomers blended with functionalized plasticizers. The functionalized plasticizers are materials such as mineral oils which contain aromatic groups, and high (greater than −20° C.) pour point compounds. Use of these compounds typically does not preserve the transparency of the polyolefin, and impact strength is often not improved.
WO 98/44041 discloses plastic based sheet like material for a structure, especially a floor covering, which contains in a blend a plastic matrix comprising a chlorine free polyolefin or mixture of polyolefins and a plasticizer characterized in that the plasticizer is an oligomeric polyalphaolefin type substance.
Other background references include EP 0 448 259 A, EP 1 028 145 A, U.S. Pat. Nos. 4,073,782, and 3,415,925.
What is needed is a polyolefin with lower flexural modulus, lower glass transition temperature, and higher impact strength near and below 0° C., while not materially influencing the peak melting temperature of the polyolefin, the polyolefin crystallization rate, or its clarity, and with minimal migration of plasticizer to the surface of fabricated articles. A plasticized polyolefin according to this invention can fulfill these needs. More specifically, there is a need for a plasticized polypropylene that can be used in such applications as food containers and toys.
Likewise, a plasticized polyolefin with improved softness, better flexibility (lower flexural modulus), a depressed glass transition temperature, and or improved impact strength (improved Gardner impact) at low temperatures (below 0° C.), where the melting temperature of the polyolefin, the polyolefin crystallization rate, or its clarity are not influenced and with minimal migration of the plasticizer to the surface of articles made therefrom is desirable.
It would be particularly desirable to plasticize polyolefins by using a simple, non-reactive compound such as a paraffin. However, it has been taught that aliphatic or paraffinic compounds would impair the properties of polyolefins, and was thus not recommended. (See, e.g., CHEMICAL ADDITIVES FOR PLASTICS INDUSTRY 107-116 (Radian Corp., Noyes Data Corporation, NJ 1987); WO 01/18109 A1).
Mineral oils, which have been used as extenders, softeners, and the like in various applications, consist of thousands of different compounds, many of which are undesirable in a lubricating system. Under moderate to high temperatures these compounds can volatilize and oxidize, even with the addition of oxidation inhibitors.
Certain mineral oils, distinguished by their viscosity indices and the amount of saturates and sulfur they contain, have been classified as Hydrocarbon Basestock Group I, II or III by the American Petroleum Institute (API). Group I basestocks are solvent refined mineral oils. They contain the most unsaturates and sulfur and have the lowest viscosity indices. They define the bottom tier of lubricant performance. Group I basestocks are the least expensive to produce, and they currently account for abut 75 percent of all basestocks. These comprise the bulk of the “conventional” basestocks. Groups II and III are the High Viscosity Index and Very High Viscosity Index basestocks. They are hydroprocessed mineral oils. The Group III oils contain less unsaturates and sulfur than the Group I oils and have higher viscosity indices than the Group II oils do. Additional basestocks, named Groups IV and V, are also used in the basestock industry. Rudnick and Shubkin describe the five basestock Groups as typically being:    Group I—mineral oils refined using solvent extraction of aromatics, solvent dewaxing, hydrofining to reduce sulfur content to produce mineral oils with sulfur levels greater than 0.03 weight %, saturates levels of 60 to 80% and a viscosity index of about 90;    Group II—mildly hydrocracked mineral oils with conventional solvent extraction of aromatics, solvent dewaxing, and more severe hydrofining to reduce sulfur levels to less than or equal to 0.03 weight % as well as removing double bonds from some of the olefinic and aromatic compounds, saturate levels are greater than 95-98% and VI is about 80-120;    Group III—severely hydrotreated mineral oils with saturates levels of some oils virtually 100%, sulfur contents are less than or equal to 0.03 weight % (preferably between 0.001 and 0.01%) and VI is in excess of 120;    Group IV—poly-alphα-olefins-hydrocarbons manufactured by the catalytic oligomerization of linear olefins having 6 or more carbon atoms. In industry however, the Group IV basestocks are referred to as “polyalphaolefins” are generally thought of as a class of synthetic basestock fluids produced by oligomerizing C4 and greater alphaolefins; and    Group V—esters, polyethers, polyalkylene glycols, and includes all other basestocks not included in Groups I, II, III and IV. (see Synthetic Lubricants and High-Performance Functional Fluids, Second edition, Rudnick, Shubkin, eds., Marcel Dekker, Inc. New York, 1999.)
Other references of interest include: U.S. Pat. Nos. 5,869,555, 4,210,570, 4,110,185, GB 1,329,915, U.S. Pat. Nos. 3,201,364, 4,774,277, JP01282280, FR2094870, JP69029554, Rubber Technology Handbook, Werner Hoffman, Hanser Publishers, New York, 1989, pg294-305, Additives for Plastics, J. Stepek, H. Daoust, Springer Verlag, New York, 1983, pg-6-69.
U.S. Pat. No. 4,536,537 discloses blends of LLDPE (UC 7047), polypropylene (5520) and Synfluid 2CS, 4CS, or 6CS having a viscosity of 4.0 to 6.5 cSt at 100° F./38° C., however the Synfluid 4CS and 8CS are reported to “not work” (col 3, ln 12).